First report of the melobesioid alga (Corallinales, Rhodophyta) M esophyllum incisllm (Foslie) Adey in South Africa

Mesophyllum incisum is reported and studied for the first time in South Africa. It has a thallus surface (SEM) with Leptophyturn-type epithallial cells. TetraJbisporangial conceptacles are mound-like and lack a peripheral rim but have a flattened pore plate. The rosette cells surrounding the tetrasporangial pores are distinct from surrounding roof cells (SEM, surface view) in being narrower, and sunken below the level of the surrounding pore plate. The cells of filaments bordering the tetrasporangial conceptacle pore canal differ from the other roof cells within the pore plate in being more elongate, narrower, and often more densely staining. Pore canal filaments also generally contain fewer cells than the surrounding filaments of the pore plate and the pore canal is more-Dr-less parallel sided. Our material agrees closely with the species as reported in Australia.

In this paper we report on M esophylfuf1l inciswn (Fostie) Adey, a species previou sly reported onl y from Au strali a, New Zealand and the subantarctic islands in that region.Although the species has been characterised byWoelkeriing and Harvey ( 1992Harvey ( , 1993) ) from Australi a, we present a desc ription of South African material here because we have additional information on the structure of the sporangial pore, and because it is important to include full descriptions of South African species towards the eventual development of a guide to the non-geniculate coralline algal flora.

Materials and Methods
South African material was collected using SCU BA diving.For scanning electron microscopy, air dried material was fractured using either fin ger nail s, fo rceps , diagonal cutters, or a small hammer and cold chi sel.Wherever possibl e a fracture perpendicular to a leading edge was used to determine internal anato my.The fractured pieces were mou nted on stubs.using adhesive tabs (Agar Scientifi c, 66a Ca mbridge Rd. , Stan stead, Essex CM24 SDA .UK), stored in a desiccator for at least 24 h prior to examin at ion, coared with gold for 4-6 min in un Edwards S150B sp utter coater.<lnd examined wi th a Hi tach i x650 scanning electron minoscope (SEM), equipped wi th a Mamiya 6 x 7 camera at an accelerating voltage of 25 KY.
For li ght microscopy, formalin preserved specimens were first decalcified in 10% nitric acid, and then secti oned at 1O-30 ).lm thickness usin g a Leitz CO 2 freezing microtome.Each individual sect ion was removed from the microtome blade using a fine sable hai r brush.and transfe red to a sl ide containing aniline blue in 50% Karo syrup.Drawings were made directly fro m prepared slides using a Ze iss microscope equipped with a drawing tube.
Conceplacle outside diameter and pore diameter were measured di rectly from the SEM.All other measu rements were made usi ng a calibrated eyepiece micrometer.In cel l measurements.length denotes the distance between primary pit connecti ons.and diameter the maximum width of the cell lumen at right angles to th is.Conceptad e measurements fo ll ow the system of Adey & Adey (1973).Thallus anatomical terminology foll ows Chamberlain (1990).while morphological term inology follows Woe lkeriing, et.Cl/.(1993).Typificati on data follow Woelkeriing (1993).
Etymology: Foslie (1906) did not exp lain the origin of the specific epithet, but 'incisum' means cut deeply and sharply (Steam 1992).How this applies to M. incisClm is uncertain.

Representative specimens examined:
- Habitat and phenology: Mesophyllum incisum is an inconspicuous cora lline that occurs in small patches on the dead parts of horny coral ske letons as well as on bryozoans, coral skeletons, and sponges.Only a few specimens were collected.All male, carposporangial and tetrasporangial conceptacles were found in March, August, and November but there are no coll ections at other times.
Distribution: Southern Africa: Cape Peninsula.World: Australia, New Zealand, South Africa, Chatham Islands, and sub-Antarctic islands south of New Zealand.Woelkerling and Harvey (1993) note that other than the type, records of this species outside of Australia have not been verified.
Habit and vegetative structure: Plants encrust mainly sponges (Figures 1-3), the horny parts of gorgonian coral, and other invertebrates , and are weakly adherent, with the margins often somewhat free.The surface is smooth and glossy and protuberances are lacking.The thallus is usually reddish purple to purplish pink, and sporangial conceptacles are sparsely distributed over the surface.They are mound-like with a flattened pore plate (Figure 18).The thallus is monomerous, measuring 250-550 ~m in thickness.Medullary filaments fonn a plumose to coaxial ventral layer (Figures 4, 5  and measure 2.5-4 ~m long x 2.5-6 ~Hn in diameter.Surfaces of epithallial cells under the SEM show thin lateral walls, and the outer wall is usually cushion-like and not sunken into an epithallial concavity (Figure 8).This outer wall is thin wi th a minute central hole that is presumed to be a scar from the pit which connected the epithallial cell during its formation to the older epithallial cell dorsal to it (Leptophytum-type surface sensu Chamberlain 1990) (Figure 8).Figures 4-7 Vegetative and male anatomy of M. illcisum (UWC).4. Diagrammatic drawing of VS of tetrasporangiai thallus showing medullnry filaments (M), cortical filaments (e), conceplacle with tetrasporangium (l), and old buried conceptaclc (K) . 5. Thallus showing epithalli aJ cells (E), subepithallial initial (1), lower cells of cortical ee) and medullary filaments (M), and cell fusi ons (1').Note that medullary filaments terminate at the base of the thallus in hyaline cells (h). 6.Male conceptacle with simple spermatangial systems on the roof (arrowhead), walls and floor (arrow) of the chamber.7. Simple spermatangial branches from the floor (F), walls (5) and roof (R) of a male conceptacle.
'with elliptical chambers that measure 3 15-380 Ilm in diameter x 135-165 J.lm in height with the roof being 80-140 ~lm thick.The fusion cell appears discontinuous in VS, with c. 5 celled gonimoblast filaments developing from the periphery (Figures 13 and  14) nnd terminating in a carposporangium, each bearing a carpospore measuring 14-20 Ilnl in length x 18-24 ~lm in diameter (measuremenfs from a si ngle specimen).
Tetrasporangial conceptacl es are sparsely distributed over the dorsal surface of the thallus.They are mound-like with a flattened pore plate (Figures 18, 19 and 21), and measure 430-550 ~lm in external diameter (Figure 19).Chambers of mature <.:onceptacJes are elliptical (Figures 15 and 21), and measure 225-400 ~lIn in diameter x 115-190 J.lm in height with the roof bcing 40-62 ~lm thick.The roof is formed from filaments interspersed among the sporangia; the lower segments of these filaments degenerate.leaving a roof composed of 3-R cells and perforated by 26-46 pores (Figure 19).Pore plugs are prescnt, and stain densely with aniline blue (Figures 15 and t  su rrounding roof (Fig ures 19 and 20).Cells of the fil aments lining the pore differ markedly from the cells which make up the rest of the roof in that they usually appear narrower, more elongate, and of(cn more densely stai ning with aniline blue (Figure 17).The pore filaments are mostly 3-4 cells long co mpared with the filaments of the rest of the pore plate which are usuall y 5-8 cells long.The pore canal measures 37-50).tm in length x 5-13 ~Im in di ameter.Tetrasporangia measure 60-170 11m in lengt h x 20-100 ~lIn in diameter (Figures 15 and 16).Old conceptacles persist and beco me bu ried in the thal lus (Figure 4), where they are often filled in by groups of elongate cells that are probably the ste rile inter-sporangiaJ fi laments.Intact sporangia are sometimes contained wi thin old buried concep tacles.Bisporangial conceptacles were not seen.

Remarks
This spec ies is characterized as follows: -thallus surface (SEM) with peripheral rim and having a flattened pore plate; -rosette cells distinct from surrounding roof cells (SEM, surface view) in being narrower, and sunken below the level of the surrounding pore plate; -cells of filaments bordering the tetraspo rangial conceptacle po re canal d iffering in s ize and shape from the cells of the other filaments wi thin the pore plate in being more elongate.
narrower, and often morc densely staining; -pore canal fi laments containing fewer cells than the sur~ rounding filaments of the pore plate; -pore canal more-or~less paralleJ sided.It is most commonly seen as a thin.delicate encrlls(alion on sponges, horny cora ls, and bryozoans.S. Afr.J. Bot. 1997.63(4)14  (T ) and pore plugs (arrowhead).16. Young (left) and matu re (right) letrasporangia.17.VS of tetrasporangial pore plate to show the cells of filaments lin ing [he pore canal (arrowhead) and pore plugs (P).Note that the cells lining the pore canal are laterall y compressed, ane fact that they arc narrower than the surrounding cells (right) of the pore plate is not always obvious (left) unless viewed in the correct plane.However, they always slain differently.as indicated by the stippling.

Key to South Afri can species of Mesophyllum
It is imporlant to verify the occurrence of all characters used in the key to con firm identiticatio n. 1. Tet ralbisporangial conceplacle pores lined by fila ments made up of cells which do not differ from those of the surrounding roof filaments 3 1.Tctralbisporang ial conccptacie pores lined by filaments made up of cells which are different from those of the surround ing roof filaments 2 2. Thall us mainly warty 10 lum py to fruticose; conceptacles found mainly on the protuberances, pore canal lined by fil aments that differ from those of the surrounding roof in having an e longate cell at their base; walls of pore canal tapering towards the surface.rosette cells flu sh with surrounding roof . . . . . . . . . . . . . . . . . . . . M. erubescens 2. Thallus mainly encrusting to warty; conceptacles found mainly on nat areas of thallus ; pore canal lined by filaments that differ from those of the surrounding roof in being narrower and more elongate; walls of pore canal more-or-Iess parallel; rosette cell s di stinct from surrou nding roof cells in being narrower, and sunken below the level of the surroundi ng pore plate (this may be difficult to see even in SEM) .
, 9 and 10) that measures 40-150 ~m in thi ckness.Cells of medullary filaments are elongate (Figures 5, 9 and 10), and measure 6-19 ~m long x 4-10 ~m in diameter.Cell fusions are abundant, occupying most of the wall of adjoining cells (Figures 5 and 10).Medullary filaments terminate at the margin in primary meri stematic cells which are usually flattened apically (Figure 9), and measure 9-22 ~m in length x 5-13 ~m in diameter.Cortical filaments form a dorsal layer 100-500 ~m thick (Figure 4).Cells of cortical filaments are elongate (Figures 5 and II), and measure 6-19 ~m in length x 4-13 ~'m in diameter.Cell fu sions are abundant and occupy most of the wall of adj oining cells (Figures 5 and II).The subepithallial initial is as long as, or longer than , the cell subtending it (Figures 5 and 11 ), measuring 4-J 8 I-lm in length x 2.5-6 I-lm in diameter.Epithallial cells occur sing ly, are more-or-Iess elliptical to dome-shaped or n at topped (Figures 5 and 11 )

Figures 1- 3
Figures 1-3 Habit photographs of M. illclsum.Reproduction: Gametangial plants are dioecious.Carpogonial conceptades were not seen, but male conceptacles and carposporaogial conceptacles have not been seen on the same thallus.Male conceptacles are conical, with elliptical chambers (Figure 6) that measure 225-400 ~m in diameter x 31 -62 ~m in height, with the roof being 56-112 ~m thick.The roof is formed from filaments that arise peripheral to the fertile area.These filaments have terminal initials, elongate more rapidly than surrounding cell s, and curve inwards to form a pore.The terminal initials of roof filaments are papillate and project into the pore at maturity (Figure 6).A layer of epithallial cells is sloughed during conceptade formation, but it may lie over the developing conceptacle until roof formation is comp lete.Unbranc hed spermatangial systems develop on the floor, walls and roof of the conceptacle (Figures 6 and 7).Carpogonial conceptacles have not been seen.Carposporangial conceptacles are conical (Figures J 2 and 13), Figures 8-11 SEM of vegetative anatomy of M. illcisum (UWC: 93/214), 8. Surface view of vegetative thallu s; note centrally located pore in flat~topped cells (arrowhead) and thin lateral walls (arrow).9. Vertical fracture of thallus at margin.showing corti cal filaments (C), medul-" lary fil aments (M).and short , flat-ropped terminal marginal initi al (arrowhead).10.Medullary cells showing cell fus ions (F) and elongate hyali ne cells at the lower surface (h).11.Ve rti cal section of outer thallus away from the margin showing corLical filaments with cell fusions (F), subepithalJi aJ initia l (i) and epithallial cell s (e).
Although characters five and six were not observed in South African specimens, they have been observed in Australian material (Woe lkeri ing & Harvey 1992).T he species sludied here lhu s conforms to Mesophyflwll on the bas is of its possession of all of the above generic characte rs.This is the fourt h species of Mesophyllum reported from South Africa (Keats & Cham berlain 1994b, Chamberlain & KealS I995).Sec Table1.
9. spcrmatangiai branches occur on the fl oor, waIls and roof o f ll1 a l ~ co ncepladcs.